1. Field of the Invention
The present invention relates to a liquid ejection head and a liquid ejection method for performing recording on a recording medium by ejecting liquid such as ink.
2. Description of the Related Art
There is an ink jet recording apparatus for performing recording on a recording medium such as paper by ejecting ink. A liquid ejection head capable of ejecting ink is generally mounted on the ink jet recording apparatus.
In the liquid ejection head, an ink ejection system using heat-generating elements is widely used. In such a liquid ejection head, heat-generating elements in multiple pressure chambers supply heat energy to ink to cause film boiling of the ink to generate bubbles in each pressure chamber. When the bubbles are generated, a pressure is applied to ink around the bubbles, and hence the ink in the pressure chamber is ejected from an ejection orifice placed so as to be opposed to the heat-generating element.
In the liquid ejection head using the heat-generating element, generally, the bubbles generated on the heat-generating element communicate with outside air flowing in the pressure chamber through the ejection orifice after the ejection of ink and are released from the ejection orifice together with the outside air. However, a phenomenon called cavitation may occur in which the generated bubbles remain on the heat-generating element, and the bubbles are pressed by the ink in a direction toward the heat-generating element to be split swiftly to the sides of the heat-generating element. When the cavitation occurs, the ink collides with the heat-generating element swiftly, and hence, the heat-generating element may be damaged.
Japanese Patent Application Laid-Open No. 2008-238401 discloses a liquid ejection head that prevents the occurrence of cavitation. In this liquid ejection head, the positions of ejection orifices are offset from those positions opposed to heat-generating elements to an opposite side of a common liquid chamber for supplying ink to pressure chambers.
According to the above-mentioned configuration, when ink is supplied from the common liquid chamber to the ejection orifice after the ejection of the ink, a flow of the ink in a direction toward the ejection orifice occurs on the heat-generating element. Therefore, bubbles generated on the heat-generating element are guided in a direction of the ejection orifice, following the flow of the ink, to communicate with outside air. Thus, in the liquid ejection head, the generated bubbles can be prevented from remaining on the heat-generating element, and hence, cavitation does not occur easily.
In recent years, there is a demand for an increase in density of ejection orifices in a liquid ejection head along with demands for higher image quality and higher speed of recording on a recording medium by a recording apparatus. In order to satisfy the demands, it is necessary to decrease the interval of the ejection orifices in an ejection orifice row formed of multiple ejection orifices and to decrease the interval of the respective ejection orifice rows.
On the other hand, in order to allow the heat-generating elements to generate sufficient heat energy, it is necessary to form each heat-generating element having at least a predetermined size. Therefore, in order to decrease the interval of the ejection orifices in the ejection orifice row, it is necessary to form the heat-generating elements in an elongated manner in a direction orthogonal to the ejection orifice row. However, in this case, as described in Japanese Patent Application Laid-Open No. 2008-238401, when the ejection orifices are placed on a downstream side of the heat-generating elements in a flow direction of the ink, the interval of the respective ejection orifice rows will become larger.